System and a method for the control of variable-ratio transmissions

ABSTRACT

A system for controlling a variable-ratio transmission is mounted on an apparatus ( 1 ) and associated with an actuator ( 2 ) for changing the transmission ratio, as well as operating means ( 3 ) for applying an input driving force to the transmission with a periodic action of given frequency. The system comprises first sensor means ( 5 ) which are sensitive to the driving force and can generate a respective first signal, second sensor means ( 6 ) which are sensitive to the spreed of operation of the apparatus ( 1 ) and can generate a respective second signal, as well as a control device ( 4 ) which is sensitive to the first and second signals and can control the actuator ( 2 ) in dependence on the first and second signals. The control device ( 4 ) is configured to determine, from the first and second signals, a reference signal indicative or a reference value of the frequency (CR). This reference signal is compared with a third signal ( 7 ) indicative of the given frequency so as to identify a corresponding deviation signal (e). The control device ( 4 ) acts on the actuator ( 2 ) in order to change the transmission ratio so as to minimize the deviation signal (e).

INTRODUCTION

The present invention addresses the problem of the control ofvariable-ratio transmissions.

A typical example of a transmission of this type, which will be referredto for simplicity in the following description, is that of a bicycletransmissions. In this connection, a method and a device forautomatically controlling the transmission ratio of a bicycle so asautomatically to identify the optimal ratio in dependence on thepedalling effort or force are known from EP-A-0 831 021.

The same subject is addressed in various other patent documents such as,for example, U.S. Pat. Nos. 5,059,158, 5,538,477, 5,356,348, 5,569,104and 5,728,017, in which it can be seen that the control may be exertedeither on the rear derailer or on the front derailer, or on bothderailers of a sports cycle.

SUMMARY OF PREFERRED EMBODIMENTS OF THE INVENTION

The object of the present invention is to improve systems forcontrolling the ratio in variable-ratio transmissions, particularly withregard to the optimization of the interaction between an apparatushaving such a transmission and an operator using the apparatus.

According to the present invention, this object is achieved by means ofa system having the specific characteristics recited in the followingclaims. The invention also relates to the respective method ofoperation.

The application of the intention if particularly advantageous in thecycling field and, in particular, in the field of competitive cycling.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described, purely by way of non-limitingexample, with reference to the appended drawings, in which:

FIG. 1 shows schematically the application of a system according to theinvention to a cycle such as a bicycle,

FIG. 2 shows the structure of a system according to the inventionschematically in the form of a block diagram,

FIGS. 3 and 4 show the general criteria of the operation of a systemaccording to the invention in two successive levels of detail,

FIG. 5 shows the operation of the system according to the invention inthe form of a flow chart, and

FIGS. 6 and 7 are further graphs indicative of the criteria (affinityfunctions) for the operation of the system.

DESCRIPTION OF ILLUSTRATIVE PREFERRED EMBODIMENTS

In FIG. 1, apparatus having a variable-ratio transmission is generallyindicated 1. In the embodiment shown, the apparatus in question isconstituted by a bicycle such as, for example, a sports cycle.

As well as comprising the parts which normally make up a bicycle of thistype (which parts clearly do not need to be described and recited indetail herein), the bicycle 1 is equipped with the following devices:

an electrically-operated gearbox 2, shown here associated with the rearderailer of the bicycle 1 (in possible variants of the invention such agearbox could alternatively or additionally be provided on the frontderailer of the bicycle, if it has one); the gearbox concerned can thuschange the position in which the bicycle chain (driven by the pedalcrank 3 by means of which the cyclist applies the input driving force tothe transmission) cooperates in a meshed arrangement with the sprocketsassociated with the rear wheel hub of the bicycle, in dependence on acontrol signal,

a control device 4, the heart of which is preferably constituted by amicroprocessor, for generating the control signal, and

a set of sensors 5 to 7 which are sensitive to respective parameters ofuse of the bicycle and can generate respective signals to be receivedand processed by the device 4; these are, basically, a sensor 5 whichcan detect the pedalling force or effort exerted by the cyclist on thepedals (that is the driving force), a sensor 6 which is sensitive to theforward speed of the bicycle 1 (in general terms, the frequency or speedof operation of the apparatus represented herein by the bicycle 1), aswell as a sensor 7 which is sensitive to the pedalling frequency, thatis, the frequency of the periodic action by which the cyclist appliesthe input driving force by means of the pedal crank 3.

Although they are theoretically separate, the various sensors inquestion may in fact be combined with one another and/or with othercomponents of the system.

For example, the sensor 7 which detects the pedaling frequency canadvantageously be combined with the sensor 5 which detects the pedallingeffort.

It should again be stated that all of the various components mentionedabove can be considered known per se (as is proved by the descriptionsin the prior patent documents cited in the introductory part of thisdescription) and/or currently available commercially. For example, agearbox 2 which can advantageously be used in the context of theinvention is constituted by the gearbox sold under the reference ZMS 800by the company MAVIC.

The block diagram of FIG. 2 shows, in schematic terms, at the level ofthe general system architecture, the arrangement of connections betweenthe various elements described above, and the control device 4 whichreceives the signals generated by the sensors 5 to 7 (also defined belowas the first, second and third signals) and which acts on the gearbox 2in order to change the transmission ratio of the gearbox 2 in dependenceon the processing operation described further below.

A set of sensors of this type (which can provide the three signalsmentioned in digital form) is available under the trade name SRMTRAINING SYSTEM from the company Ingenieurbüro Schoberer.

The further functional blocks indicated 8 and 10 indicate that themethod according to the invention allows the user to intervene in theoperation of the system, in particular with regard to two basic factors,that is:

the way in which the device 4 interprets or classifies (as will bedescribed further below) the values of the signals received from thesensors 5 to 7, and

the processing logic implemented by the device 4 with a view to actingon the gearbox 2.

In particular, in the currently-preferred embodiment, the systemaccording to the invention allows the following factors to be taken intoaccount, by respective selective control interventions;

the cyclist's level of preparation and fitness (module 8),

the riding or racing strategy adopted by the cyclist (module 9) and, ingeneral,

the rules which the user intends to be followed in the automaticmanagement of the transmission control function (module 10).

BASIC PRINCIPLES THE INVENTION

Before proceeding with the detailed description of a possible embodimentof the invention, it seems useful to describe briefly the basicprinciples upon which the invention is based. This will be done withspecific reference to its possible application in the cycling field.

It is a fact that, for given peripheral conditions (physicalcharacteristics, athletic preparation, type of bicycle, gradient of theroad and atmospheric conditions; e.g. opposing or favouring wind, etc.),the maximum power which a cyclist can transfer to the bicycle isachieved in the region of a very precise pedalling frequency which inpractice is identified by the speed of rotation (revolutions per minuteor rpm) imparted to the pedal crank.

This is due to the fact that, given a certain resisting load, there isalways an optimal impedance match between the resisting load and thefrequency such as to maximize the power produced, that is, to maximizeefficiency.

These remarks are confirmed by numerous scientific works such as, forexample:

Gregor, R. J. and Rugg S. G. (1986), “Effects of saddle height andpedalling cadence on power output and efficiency”, in E. R. Burke (Ed.),Science of cycling (pp. 69-90). Champaign, IL: Human Kinetics;

Kyle C. R. and Caiozzo, V. J. (1986), “Experiments in human ergometry asapplied to the design of human powered vehicles”, International Journalof Sports Biomechanics, 2, 6-19; and

Allan V. Abbott and David Gordon Wilson (1995), “Human-PoweredVehicles”, (p. 35-37), IL: Human Kinetics.

For a given resisting load, the bicycle enables a condition of impedancematch, and hence an optimal frequency to be selected by changing thetransmission ratios. In practice, the cyclist is comparable to ahigh-efficiency motor which can produce its best output in terms ofpower produced within a fairly narrow band of pedalling frequencies (orcadences) By altering the ratios, the cyclist can keep his pedallingaction within this band of greatest efficiency. In practice, if thefrequency is too low (below 60/75 rpm), the risk of muscle damageincreases, whereas if it is too high (90/120 rpm) the cyclist starts togo into oxygen deficit.

By way of direct conceptual reference (but this should not be seen asindicative of a precise analogy of the functional blocks) the criterionof maximizing the power output by arranging for the cyclist always to beable to pedal at the optimal frequency can be represented in the form ofthe control diagram shown in FIG. 3.

In this diagram, block 1 indicates the bicycle system as a whole. Theoperating conditions of the system are determined (with regard to thetransmission ratio) by what may be defined, by the conventionalterminology of automatic control theory, as an “actuator” (constituted,in the specific example, by the gearbox 2). The control system, shownschematically in the form of the device 4, can therefore act on theactuator 2 (in dependence on the signals of the sensors, as shown bestin the diagram of FIG. 4 which will be referred to below) so as toimplement a feedback operation directed towards minimizing the deviationor error “e” which may be found between a theoretical referencefrequency CR and the actual frequency determined from the correspondingsignal generated by the sensor 7.

In practice, when the error signal (e) is above a predetermined,possibly variable, threshold, this causes the actuator 2 to be driven ina manner such as to change the transmission ratio so as to bring thesignal (e) back below the predetermined threshold. In practice (speakingin deliberately schematic terms) the transmission ratio (understood asthe ratio between output speed and input speed) is reduced when thepedalling frequency tends to fall (for example, because the cyclist ispedalling uphill or against the wind) and is increased when thefrequency tends to rise (for example, because the cyclist is pedallingdownhill or with a favourable wind).

From this last point of view, the method according to the invention maybe implemented either with the use of the specific criteria describedfurther below with reference to FIG. 5 and the following Figures(basically with the use of a so-called expert system, preferably of the“fuzzy” type) or, in less preferred embodiments, by adopting systemswhich perform the control operation (action on the gearbox/actuator 2 soas to minimize the deviation between the reference frequency CR and theactual pedalling frequency) with the use of mechanisms of differenttypes for processing the signals, for example, of the type described inthe various documents cited in the introductory part of the presentdescription.

DETAILED DESCRIPTION OF AN EMBODIMENT OF THE INVENTION

The important element of the invention is that, instead of providing foroperation on the basis of a reference frequency value CR which is fixedor predetermined (possibly selectively) the system according to theinvention determines the reference frequency value CR (in accordancewith a substantially adaptive criterion, preferably implemented in realtime or substantially in real time) by deriving the reference frequencyfrom the very parameters (pedalling effort, forward speed, actualpedalling frequency, etc.) which characterize the interaction betweenthe cyclist and the bicycle at the time in question. All of this takesplace in accordance with intervention criteria which can be determinedand controlled selectively by the user.

The importance of this factor can be understood better if it is notedthat the reference frequency CR is not static and determinable a priori,even selectively. In fact it depends, on the one hand, upon theresisting load (which in turn depends on various factors) and, on theother hand, on further external factors.

For example, the dependence of the reference frequency CR on theresisting load may be expressed as a dependence on factors such as:

the torque exerted on the pedal crank (the torque required to maintain aconstant speed varies with variations of the characteristics of thetrack), and

the speed (aerodynamic resistance, which is a function of the square ofthe speed, increases as the speed increases).

Dependence on other factors, on the other hand, includes factors suchas, for example:

racing strategy: the cyclist may decide to pedal for a race, for asprint, or simply for a tiring translocation, in accordance withcriteria which express his will, and hence a basically predictivebehaviour projected into the future and not based on parameters detectedand/or detectable in the past or in the present, and

the cyclist's level of preparation; the more the cyclist has trained andprepared, the better he will be able to sustain high frequencies, orlower frequencies but with greater effort produced.

The control device 4 preferably comprises a so-called expert systemoperating in accordance with a fuzzy logic. The fuzzy logic and therespective operating mechanisms are known per se, as are the advantageswhich this type of logic brings to complex problems the solution ofwhich is based more on empirical considerations resulting fromexperiment and simulation than on mathematical modelling of the problem.

For general information on these subjects, for example, the referencework by Mohammad JAMSIDI, Nader VADIEE, and Timothy J. ROSS—“Fuzzy LogicAnd Control” (1993)—IL: Prentice Hall, may usefully be consulted.

The flow chart of FIG. 5 shows a sequence of steps, between an initialstep 100 and a final step 101, which is intended to be repeated by thecontrol device 4 in order to perform an automatic control of theactuator constituted by the gearbox 2 and hence of the transmissionratio of the bicycle.

The reference to automatic operation does not, however, mean that abicycle 1 equipped with the system according to the invention shouldnecessarily provide only for automatic operation. As in known systems,the cyclist can in fact exclude the operation of the system so as to beable to act on the transmission unit or transmission units manually inconventional manner (it is pointed out once more that the methodaccording to the invention way be applied only to one or to both of thederailers normally provided on a sports cycle) or to provide for someform of semi-automatic operation. In any case, these methods ofoperation and of complete or partial deactivation of the system are suchas not to require detailed description herein.

To concentrate attention on automatic operation, it is pointed out againthat the sequence of steps between steps 100 and 101 can be implementedwith a periodic cadence and/or at a certain frequency which may be fixedor variable according to need, in dependence on specific requirements ofuse. In particular, the frequency of repetition of the steps describedbelow does not need to be very high since, even in transitory racingstages, changes in the bicycle system 1 develop fairly slowly over timewhen compared with the processing speed of conventional electronicapparatus. The above-mentioned control sequence may be repeated, forexample, at intervals of about 1 second.

The action on the gearbox 2 in order to change the transmission ratiopreferably provides for a certain low-pass filtering effect. This is toprevent instantaneous variations of one or more of the parameters usedby the expert system 41 being translated into an undesired immediatechange of the transmission ratio: for example, there might be a suddenchange in the pedalling effort due to the fact that the cyclist hasrisen from the saddle upon starting to pedal, so to speak “standing” onthe pedals; above all, the above-mentioned change may have a differentsign in dependence on the instantaneous angular position of the pedalcrank at the moment at which the cyclist starts to pedal standing up.Moreover, it seems advantageous, in any case, to prevent changes intransmission ratio, possibly with opposite signs, taking place in rapidsuccession.

The description of the operation of the expert system 41 will be givenbelow, upon the assumption that the expert system receives at its inputexclusively the signals corresponding to the pedalling force or effort(sensor 5) and to the speed of the bicycle (sensor 6). This selection isdictated both by reasons of simplicity of description and by theconsideration that a skilled person familiar with the design andconstruction of expert systems will certainly have no difficulty in alsoincluding the third parameter (actual pedalling frequency) in theoperation of the system. However, this latter parameter may be used bythe expert system purely to perform, at the node indicated 42 in FIG. 4,a comparison between this parameter and the reference frequency CRdefined by the expert system on the basis of the signals coming from thesensors 5 and 6 and in order to calculate the current gear ratio 2, ifit is not available by other means.

In other words, the expert system 41 may take account of the signalcorresponding to the actual pedalling frequency in at least twodifferent ways, that is:

on the basis of the method shown in FIG. 5, by identifying the signalcorresponding to the reference frequency CR solely on the basis of thepedalling effort signal and of the speed signal, using the signalcorresponding to the actual pedalling frequency coming from the sensor 7purely for generating the error signal (signal e) used to control thegearbox 2, and

on the basis of a variant, not shown explicitly, also using the signalrelating to the actual pedalling frequency to define the referencefrequency CR.

Basically, the expert system 41, operating in accordance with a fuzzylogic, converts the values of the input variables (for example, thesignals read from the sensors 5, 6 and—possibly—7) into a linguisticdescription in order then to work out a control strategy contained in aset of logic rules. The result is then converted back into a precise andunambiguous output datum.

With reference to the flow chart of FIG. 5, the steps indicated 102 and103 indicate the initial steps in which the system reads the signalscoming from the sensor 5 (pedalling effort) and the sensor 6 (speed),respectively. These are preferably signals already converted intodigital form beforehand at the outputs of the respective sensors, as isthe case in the SRM sensors already mentioned above. If this is not thecase, the conversion is performed, in knowm manner, in the device 4.

In the subsequent steps 104, 105, the expert system converts each of thetwo variables read as inputs into fuzzy values, that is, linguisticvalues such as “high”, medium”, “low”, medium-high”, etc. In order toperform these attributions, it makes use of predefined functions whichreflect the degree of affinity of the fuzzy variables to the variousfuzzy values (affinity functions).

The affinity function relating to speed preferably has a curve of thetype shown in FIG. 6 in which the abscissa scale corresponds to thespeed value (sensor 6) expressed in km/h. It should be noted that thereare 5 fuzzy values (linguistic values: B=low, MB=medium low, M=medium,MA=medium high, A=high).

The affinity function relating to torque preferably has a curve of thetype shown in FIG. 7 in which the abscissa scale corresponds to thevalue of the pedalling torque (pedalling effort or force—sensor 5)expressed in N.m. There are 4 fuzzy values (B, MB, M, A).

Again, it should be stated that the steps illustrated by boxes 102 to105 have been shown as theoretically performed by a parallel processingmethod for each input parameter since this representation is, above all,more readily understood. It will be clear to experts that the sameresult can be achieved by serial processes.

It will also be noted that the flow chart of FIG. 5 makes clear that itis possible to intervene in steps 104, 105 by means of commands appliedby the user by means of interface modules 8, 9 and 10. These interfacesmay in fact be incorporated in a user interface 11 such as, for example,a keypad or an analogue control module disposed, for example, on thehandlebars (FIG. 1) in a position readily accessible to the cyclist.

The logic of the attribution of linguistic values to the datacorresponding to the signals coming from the sensors 5 and 6 may in factvary in dependence on various parameters set selectively on theinterface modules 8, 9, 10.

For example, the cyclist's level of athletic preparation (module 8) maymean that a speed or a pedalling effort which is to be considered highfor an amateur or recreational cyclist may be considered differently(for example, medium-high, medium or even low) for a professionalcyclist.

In exactly the same way, with reference to the function of the module 9,to which a role of identifying racing strategy has been attributed,clearly, a speed and/or pedalling effort value considered high during atranslocation stage, even within a cycling race, may be considered lowor even very low with reference to a sprint or a timed race.

The foregoing also applies in identical manner to the module 10 whichsupervises the general definition of the rules of operation of theexpert system. In this case, the intervention may, for example, be thatof intervening in the operation to define the above-described affinityfunctions by removing or adding affinity functions; an amateur orrecreational cyclist will usually be less interested in a verysophisticated differentiated definition of the above-mentioned functionsthan a professional for whom the need continuously to achieve a closeadaptation of the bicycle system to his physical performance may be verypressing and decisive.

The box indicated 106 represents schematically the set of functions ofthe expert system dedicated to the definition of the reference frequencyas a result of the attribution of the affinity functions performed insteps 104 and 105.

In a possible embodiment (which is known per se to experts in the designof these systems and therefore does not require a detailed descriptionherein), the criterion for the application of the above-mentioned rulesmay be regarded as a type of scanning of a matrix table, for example, atwo-dimensional table of which the lines are identified by the affinityfunctions relating to the speed and the columns are identified by theaffinity functions relating to the pedalling effort. With reference tothe examples given in FIGS. 6 and 7 (which provide for five and fourfuzzy values, respectively), there may be 5×4=20, or more correspondingrules. If the parameter relating to the actual pedalling frequency isalso present, the corresponding affinity functions identify the thirddimension of the matrix structure (which in any case is implemented withfuzzy logic and hence with respective boxes identified by probabilityfunctions).

The rules implemented in box 106 can be written in explicit form in thefollowing manner:

A) if the speed is LOW and the torque is HIGH THEN the referencefrequency is LOW

B) if the speed is MEDIUM LOW and the torque is HIGH THEN the referencefrequency is MEDIUM LOW

C) if the speed is LOW and the torque is MEDIUM THEN the referencefrequency is MEDIUM LOW

D) if the speed is MEDIUM LOW and the torque is MEDIUM THEN thereference frequency is MEDIUM LOW etc.

In terms of the value (VALCR) of the reference frequency value CR, theoutput fuzzy values could be:

VALCR LOW=68 rpm

VALCR MEDIUM LOW=78 rpm

VALCR MEDIUM=86 rpm

VALCR MEDIUM HIGH=92 rpm

VALCR HIGH=95 rpm

Naturally, as is well known to experts in the design of fuzzy systems,the system may also conclude that, in certain conditions, the value“medium” should be attributed to the reference frequency CR at 25% and“low” at 90%. As is well known to experts in fuzzy logic, each fuzzyvalue is independent of the others so that it is wholly legitimate forthe system to reach the conclusions set out above, that is, with a sumof the fuzzy values other than 100%.

It will also be appreciated that—in accordance with per se knowncriteria—the set of functions indicated schematically by the block 106may be rendered variable in dependence on the parameters set by the userby acting on the interface 11; this applies in particular with regard tothe possibility of modifying the rules which determine the attributionof the reference frequency value in dependence on the affinity functionscorresponding to the input parameters so as to be able to implementdifferent sets of rules.

It is also possible to provide—in accordance with known criteria—for theexpert system 41 to be able to store the above-mentioned set of rules orpossibly several sets of rules to be used in different conditions, independence on learning cycles, that is, to provide for a stage for thetraining of the system in which the cyclist acts on the transmission,changing the ratios by means of a positive action by the cyclist (anexpression of his will) in dependence on various riding conditionswhilst the system learns the respective rules, subsequently applyingthem automatically when this operating criterion is subsequentlyselected.

The above-mentioned control mechanism and, in particular, the learningmechanism, may be implemented with the use of the configurationscurrently known as neural or neurone networks which, as is well known,can be applied well to the implementation (and to the learning) ofoperating data and conditions which are purely phenomenological andcannot be expressed directly in the form of a mathematical model,particularly of an algorithmic type.

In the step indicated 107, the expert system 41 implements a reverseconversion mechanism known as “defuzzyfication” in which the fuzzyvalues of the output variable are combined to produce a precise value ofthe reference frequency parameter CR.

The operating criteria described above can be understood even better onthe basis of the practical example described below.

PRACTICAL EXAMPLE

At a given moment, the speed value (sensor 6)=17 km/h and the torquevalue (sensor 5)=37 N.m are measured.

From the first affinity function it is found that:

LOW speed=0.7777

MEDIUM LOW speed=0.2222

MEDIUM speed=0

MEDIUM HIGH speed=0

HIGH speed=0

From the second affinity function it is found that:

LOW torque=0

MEDIUM LOW torque=0

MEDIUM torque=0.3125

HIGH torque=0.6875

From rule A)→LOW reference frequency=min (0.7777, 0.6875)=0.6875

From rule B)→MEDIUM LOW reference frequency=min (0.2222, 0.6875)=0.2222

From rule C)→MEDIUM LOW reference frequency=min (0.7777, 0.3125)=0.3125

From rule D)→MEDIUM LOW reference frequency min=min (0.2222,0.3125)=0.2222

Thus, by combining the result of rule A with itself:

LOW reference frequency=0.6875.

By combining the result of rules B), C), D)→MEDIUM LOW referencefrequency=max. (0.2222, 0.3125, 0.2222)=0.3125 .

At this point it is necessary to apply defuzzyfication, starting fromthe fuzzy output values Reference frequency:

LOW=0.6875

MEDIUM LOW=0.3125

MEDIUM=0

MEDIUM HIGH=0

For example, if${Cr} = \frac{\sum\limits_{i = 1}^{5}{{CR}_{1} \cdot {VALCR}_{i}}}{\sum\limits_{i = 1}^{5}{CR}_{i}}$

it follows that${CR} = {\frac{{0.6875 \cdot 68} + {0.3125 \cdot 78} + 0.86 + 0.92 + 0.95}{0.6875 + 0.3125 + 0 + 0 + 0} = {\frac{71.25}{1} = 71.25}}$

With reference once more to the flow chart of FIG. 5 in step 108, thereference frequency value thus obtained is compared (as also shown morespecifically at the node 42 which is actually included in the expertsystem 41) with the pedalling frequency value derived by the sensor 7.

If the respective modulus of the deviation (error signal “e”) is below agiven threshold, the system does not intervene, going on to the finalstep 101, thus deciding in practice not to act on the gearbox 2 and thatthe question of a possible change of the transmission ratio is to bereconsidered upon the next checking sequence.

If, however, it is detected that the amount of the deviation value isabove the given threshold and therefore such as to require intervention,the system goes on to a further step 109 and then to yet anothersubsequent step 110, in which the action on the gearbox 2 is actuallyimplemented so as to bring about the change in ratio (an increase or adecrease) in dependence on the adaptation requirements found, that is,in dependence on the sign of the deviation value “e”.

The step indicated 109 (which is optional and may in any case also beimplemented in another form, for example, simply by going to the finalstep 101) corresponds to a time check (in practice a filteringmechanism) in which the device 4 ascertains that an adequate period oftime has elapsed since the preceding change in ratio. If a period oftime less than a predetermined time threshold has elapsed (negativeresult of the comparison step 109) the system goes directly to the finalstep 101 without acting on the gearbox 2, postponing any ratio changingoperation to a subsequent control sequence.

If, however, an adequate period of time has elapsed, the system goes onto step 110, changing the transmission ratio.

With reference to step 109, it has been explained that by acting on theinterface 11 and, in particular, on the module 10 (relating to thechanging of the operating rules of the system) the cyclist canselectively vary the value of the time threshold used to perform thefiltering function.

In this case also, whereas an amateur or recreational cyclist mayconsider it preferable to have a sufficiently long period of time (inparticular to avoid having too “sensitive” a system which changes thetransmission ratio every time the need to act in this sense isrecognized, even for short periods of time), a professional cyclist whois more skilled and practised in evaluating and controlling his physicalperformance may wish to reduce this period, possibly greatly, so as tohave a system which can adapt very quickly to different ways adopted bythe cyclist for interacting with the bicycle system 1.

Naturally, the principle of the invention remaining the same, thedetails of construction and forms of embodiment may be varied widelywith respect to those described and illustrated, without therebydeparting from the scope of the present invention.

What is claimed is:
 1. A system for controlling a variable-ratio transmission mounted on an apparatus (1), the transmission being associated with: an actuator (2) for changing the transmission ratio, and operating means (3) for applying an input driving force to the transmission by a periodic action of given frequency, the system comprising: the first sensor means (5) which are sensitive to the driving force and can generate a respective first signal, second sensor means (6) which are sensitive to the speed of operation of the apparatus (1) and can generate a respective second signal, and a control device (4) which is sensitive to the first signal and to the second signal and which can control the actuator (2) in dependence on the first signal and the second signal, and the system including that: third sensor means (7) which are sensitive to the given frequency and which can generate a respective third signal are provided, the control device (4) is configured to determine, from at least the first signal and the second signal, a reference signal indicative of a reference value for the frequency (CR), the control device(4) can compare (42, 108) the reference signal and the third signal so as to identify a corresponding deviation signal (e), and the control device (4) is configured to act on the actuator (2), changing the transmission ratio so as to minimize the deviation signal (e).
 2. A system according to claim 1, including that: the first sensor means (5) comprise a device for measuring the pedalling force applied to a pedal crank (3) of a bicycle (1) and the second sensor means comprise a sensor for detecting the forward speed of the bicycle (1), and the control device (4) is a control device which can act on at least one gearbox (2) mounted on the bicycle (1).
 3. A system according to claim 1, including that the control device (4) is configured so as to determine the frequency reference signal (CR) also in dependence on the third signal.
 4. A system according to claim 1, including that the control device (4) comprises: a first functional module (104) which is sensitive (102) to the first signal and can classify the first signal in dependence on a respective first degree of affinity, a second functional module (105) which is sensitive (103) to the second signal and can classify the second signal in dependence on a respective second degree of affinity, a third functional module for the application of rules (106), which is sensitive to respective values of the first and second degrees of affinity and can determine the frequency reference value (CR) with values differentiated in dependence on the values of the first and second degrees of affinity.
 5. A system according to claim 4, including that it comprises at least one control module (8, 9, 10) operable selectively in order to vary selectively at least one of: a criterion for the attribution of the first degree of affinity by the first functional module (104), a criterion for the attribution of the second degree of affinity by the second functional module (105), and a law for the determination of the frequency reference value (CR) by the third functional module (106) from the degrees of affinity attributed by the first functional module (104) and the second functional module (105) and the first and second signals.
 6. A system according to claim 4, including that the first, the second and the third functional modules (104, 105, 106) operate in accordance with a fuzzy logic.
 7. A system according to claim 5 including that the at least one control module (8, 9, 10) comprises at least one of: a first functional control module (8) for selectively varying the criterion for the attribution of the first and second degrees of affinity by the first and second functional modules (104, 105) in dependence on the cyclist's athletic level, a second functional control module (9) for selectively varying the criterion for the attribution of the first and second degrees of affinity by the first and second functional modules (104, 105) in dependence on various strategies for the riding of the bicycle (1), and a third functional control module (10) for selectively varying the rules for determining the frequency reference value (CR) given by the third functional module (106).
 8. A system according to claim 1, including that the control device (4) includes a function (109) for inhibiting action on the actuator (2) for a period of time of predetermined duration starting from the preceding action performed by the control device (4) on the actuator (2) in order to change the transmission ratio.
 9. A system according to claim 8, including that the duration of the time interval is variable selectively.
 10. A method of controlling a variable-ratio transmission mounted on an apparatus (1), the transmission being associated with: an actuator (2) for changing the transmission ratio, and operating means (3) for applying an input driving force to the transmission by a periodic action of given frequency, the method comprising the steps of: detecting (5) the driving force and generating a respective first signal, detecting (6) the speed of operation of the apparatus (1) and generating a respective second signal, and controlling the actuator (2) in dependence on the first and second signals, and including that it comprises the steps of: detecting (7) the given frequency and generating a respective third signal, determining, from at least the first signal and the second signal, a reference signal indicative of a reference value (CR) for the frequency, comparing (42, 108) the reference signal and the third signal so as to identify a corresponding deviation signal (e), and controlling the actuator (2), changing the transmission ratio so as to minimize the deviation signal (e).
 11. A method according to claim 10, including that it comprises the steps of: generating the first signal as a signal indicative of the pedalling force applied to a pedal crank (3) of a bicycle (1), generating the second signal as a signal indicative of the forward speed of the bicycle itself (1), and controlling, as the actuator (2), at least one gearbox mounted on the bicycle (1).
 12. A method according to claim 10, including that it comprises the step of determining the frequency reference value (CR) also in dependence on the third signal.
 13. A method according to claim 10, including that it comprises the steps of: classifying (104) the first signal in dependence on a respective first degree of affinity, classifying (105) the second signal in dependence on a respective second degree of affinity, and determining the frequency reference value (CR) with values differentiated in dependence on the values of the first and second degrees of affinity.
 14. A method according to claim 13, including that it comprises the steps of selectively varying at least one of: a criterion for the attribution of the first degree of affinity, a criterion for the attribution of the second degree of affinity, and a law for the determination of the frequency reference value (CR) from the degrees of affinity attributed to the first and second signals.
 15. A method according to claim 14, including that the criteria for the attribution and the law for the determination are based on a fuzzy logic.
 16. A method according to claim 11, including that it comprises at least one of the steps of: selectively varying the criterion for the attribution of the first and second degrees of affinity in dependence on the cyclist's athletic level, selectively varying the criterion for the attribution of the first and second degrees of affinity in dependence on various strategies for the riding of the bicycle, and selectively varying the rules for the determination of the frequency reference value (CR) from the degrees of affinity.
 17. A method according to claim 10, including that it comprises the step of inhibiting action on the actuator (2) for a period of time of predetermined duration starting from the preceding action performed on the actuator in order to change the transmission ratio.
 18. A method according to claim 17, including that the duration of the period of time is variable selectively. 